1. Field
Embodiments relate generally to sodium containing glasses and more particularly to fusion formable silica and sodium containing glasses which may be useful in photochromic, electrochromic, Organic Light Emitting Diode (OLED) lighting, or photovoltaic applications, for example, thin film photovoltaics.
2. Technical Background
Recent interest in the higher efficiencies offered by thin film photovoltaics has spawned considerable efforts into the development of new glass substrates and superstrates tailored to the needs of this new market. The thin film photovoltaics manufacturing processes typically require substrates capable of handling elevated temperatures for extended periods of time without warping, making glasses particularly well suited for these applications. Additionally, some thin film photovoltaic processes (such as CIGS) desire sodium to diffuse from the glass into the deposited layers, making sodium-containing glasses even more desirable for particular applications.
Existing glasses (such as soda lime or display compositions) have been used to demonstrate extremely high efficiencies in this field but the use of any glasses designed for other applications is wrought with problems. For example, soda lime glass offers a cheap, readily available sodium-containing substrate but its low strain point drastically inhibits its use in the higher temperature process that allow thin film photovoltaic processes to reach their highest efficiencies.
The use of glasses designed for display applications provides the required high strain point but the coefficient of thermal expansion (CTE) of these glasses is often too low to allow the reliable construction of large photovoltaic panels due to CTE mismatch with the photovoltaic films. Additionally, many glasses designed for display applications are intentionally alkali-free, making them less useful for those thin film photovoltaic applications desiring sodium diffusion from the glass.
In some thin film photovoltaic applications, it would be advantageous to have a sodium-containing glass sheet with a high strain point and a high CTE. Further, it would be advantageous to have a sodium-containing glass with a high strain point and high CTE that is fusion formable to allow processing into a flat sheet with optimal surface characteristics.